How can a village become a city?

Answer 1

The legal distinction between "village" and "city" varies from location to location. It's fairly common for a collection of houses in an unincorporated areas to be a "village", while "city" is an incorporated area with definite boundaries, at least a certain population within those boundaries (exactly what the limit is again varies), and possibly with a certain form of government, that has chosen to call itself a city.

So the best answer is to consult the law in your area to see what the definition of "city" is.